Study finds codeine might increase pain sensitivity

A study has found using codeine might cause a heightened sensitivity to pain, rather than relief.

An Adelaide University study has compared the impact and effects of codeine and morphine on patients.

The researchers say their findings raise worries that codeine use could be a problem for chronic pain sufferers who need long-term medication.

For nine years, Liz Dawson, 53, has struggled with severe migraines and headaches.

Like many, she buys over-the-counter tablets containing codeine to ease the pain.

"In the beginning it helped dramatically, it knocked it on the head. I never went on anything more heavy, so the Panafen had got me through the worst of that pain," she said.

"But I found that as the years went on the more often I took it, the worse the headaches seemed to get."

In between the migraines she experienced three to four times a month, Ms Dawson said headaches began to appear.

"It was almost constant. It was a rare day when I didn't actually have some kind of headache," she said.

Ms Dawson thought her use of codeine might be doing more harm than good.

That was consistent with the finding of the South Australian study which compared the pain-relieving and pain-worsening effects of codeine and morphine.

Jacinta Johnson is a pharmacist and PhD student at Adelaide University.

"We found that after receiving codeine on a regular basis there was actually increased sensitivity to pain compared to before the drug was used at all so, even though the codeine provides less pain relief than the morphine did, we found that both the codeine and the morphine produced the same increase in sensitivity," she said.

Temperature, touching and brushing caused pain

It's difficult to work out exactly how long is too long to be taking it, but it seems to be more of a problem if you're taking it for sort of months at a time and taking it very regularly within that time

Researcher Jacinta Johnson

The researchers found patients using codeine long-term were more sensitive to things that were normally painful, such as higher temperatures, but also to things that should not cause pain at all, like soft touching of the skin or brushing of hair.

For migraine sufferers like Liz Dawson, there were more headaches, more often.

Jacinta Johnson said it was still not clear what the safety limits were on how often codeine should be taken.

"It's difficult to work out exactly how long is too long to be taking it, but it seems to be more of a problem if you're taking it for sort of months at a time and taking it very regularly within that time, so day-in day-out rather than if you just take it occasionally," she said.

She said the main concern was that such painkillers could be bought without a prescription.

"One in five Australians will suffer from chronic pain at some point in their life and, of those patients, about one in three of them will use these stronger painkillers like codeine and morphine," she said.

Dr Deon Schoombie is from the Australian Self Medication Industry, which represents manufacturers of over-the-counter medicines.

"It's very clear on the pack, the instructions, that it is only for short-term use. The pack sizes have been restricted to five days' [supply] and there's a clear warning saying if you need it for longer it should only be under supervision of medical practitioners," he said.

Jacinta Johnson said there were currently few effective alternatives to codeine in over-the-counter pain medication.